linux-kernel - Re: [PATCH] dt-bindings: mmc: fsl-imx-esdhc: allow more compatible combinations

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Date:   Sun, 8 Jan 2023 15:45:44 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Andreas Kemnade <andreas@...nade.info>
Cc:     ulf.hansson@...aro.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, shawnguo@...nel.org,
        s.hauer@...gutronix.de, kernel@...gutronix.de, festevam@...il.com,
        linux-imx@....com, linux-mmc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dt-bindings: mmc: fsl-imx-esdhc: allow more compatible
 combinations

On 07/01/2023 16:54, Andreas Kemnade wrote:
> On Sat, 7 Jan 2023 16:07:35 +0100
> Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:
> 
>> On 07/01/2023 16:01, Andreas Kemnade wrote:
>>> On Sat, 7 Jan 2023 15:09:24 +0100
>>> Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:
>>>   
>>>> On 07/01/2023 15:07, Andreas Kemnade wrote:  
>>>>> On Sat, 7 Jan 2023 15:00:56 +0100
>>>>> Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:
>>>>>
>>>>> [...]    
>>>>>>>> I asked to remove half-compatible. Not to enforce.
>>>>>>>>      
>>>>> so you are saying that allowing
>>>>> compatible = "A", "B" 
>>>>> is not ok, if B is not fully compatible. I agree with that
>>>>> one.    
>>>>
>>>> I did not say that. It's not related to this problem.
>>>>  
>>> You said "I asked to remove half-compatible" that means to me
>>> remove "B" if not fully compatible with A which sounds sane to me.
>>>   
>>>> Again - you cannot have device which is and is not compatible with
>>>> something else. It's not a Schroedinger's cat to be in two states,
>>>> unless you explicitly document the cases (there are exception). If this
>>>> is such exception, it requires it's own documentation.
>>>>  
>>> so conclusion:
>>> If having A and B half-compatible with A:
>>>
>>> compatible = "A" only: is allowed to specifiy it the binding (status quo),
>>>   but not allowed to make the actual dtsi match the binding documentation
>>>   https://lore.kernel.org/linux-devicetree/72e1194e10ccb4f87aed96265114f0963e805092.camel@pengutronix.de/
>>>   and
>>>   https://lore.kernel.org/linux-devicetree/20210924091439.2561931-5-andreas@kemnade.info/
>>>
>>> compatible = "A", "B" in the binding definition: is not allowed ("I asked to remove
>>>    half-compatible" (= removing B))  
>>
>> No, half compatible is the A in such case.
>>
> I think that there is some misunderstanding in here. I try once again.
> 
> Define compatible with "X" here:
> To me it means:
> 
> device fully works with flags defined in:
> 
> static const struct esdhc_soc_data usdhc_X_data = { ... };
> 
> with usdhc_X_data referenced in
>         { .compatible = "X", .data = &usdhc_X_data, },
> 
> 
> So if there is only "A" matching with above definition of compatibility
>   compatible = "A" would sound sane to me.
> 
> And scrutinizing the flags more and not just wanting to achieve error-free
> dtbs_check, I think is this in most cases where there is only "A". 
> 
> If there is "A" and "B" which match that compatibility definition, you
> say that only compatible = "A", "B" is allowed, but not compatible = "A".
> In that case I would have no problem with that.
> 
> But if there is only "A" but no "B" matching the above definition, I would expect
> that only compatible = "A" is allowed but *not* compatible = "A", "B".

Sorry, I don't follow. I also do not understand what "matching" means in
these terms (binding driver? of_match?) and also I do not know what is
the "above definition".

Devicetree spec defines the compatibility - so this is the definition.
There will be differences when applying it to different cases.

Best regards,
Krzysztof